The present invention generally relates to a die casting method and machine, and more particularly to a die casting method and machine in which products each having a complex shape can be accurately and effectively cast in aluminum alloy or the like.
Aluminum alloy, magnesium alloy or the like is cast by a die casting machine as shown in FIGS. 1A through 1D. This die casting machine has a fixed die 111 and a movable die 112. A cavity 119 and a runner 121 are formed between the surfaces of the fixed die 111 and the movable die 112 when the fixed die 111 and the movable die 112 are connected to each other. The cavity 119 has a shape corresponding to a product. Molten metal flows through the runner 121 to the cavity 119. A core 115 is provided in the movable die 112 so as to be capable of moving forward and backward with respect to the cavity 119. The fixed die 111 is provided with a sleeve 113. A plunger 114 is provided in the sleeve 113 so as to extrude the molten metal 117 from the sleeve 113 and inject it into the cavity 119. The movable die 112 is provided with a rapping bar 116 for pushing out the product from the movable die 112.
The above die casting machine casts aluminum alloy, in general, in accordance with a procedure shown in FIGS. 1A through 1D.
(1) CLAMPING DIES
The movable die 112 is brought into contact with the fixed die 111, as shown in FIG. 1A, and then the movable die 112 and the fixed die 111 are clamped together at a predetermined clamping pressure.
(2) SUPPLYING MOLTEN METAL
After the above clamping dies process is completed, molten metal 117 formed of an aluminum alloy or the like is supplied to the sleeve 113.
(3) INJECTION
Next, the molten metal 117 is extruded by the plunger 114 from the sleeve 113 and injected via the runner 121 and a gate 118 into the cavity 119 formed between the dies 111 and 112 which are clamped together, as shown in FIG. 1B. The plunger 114 injects the molten metal 117 into the dies 111 and 112 at a predetermined injection pressure and a predetermined injection speed.
(4) SEPARATING DIES
After the plunger 114 presses the molten metal 117 at the predetermined pressure for a predetermined time, the movable die 112 moves backward so as to be separated from the fixed die 111, as shown in FIG. 1C. At this time, the core 115 is pulled out from the cavity 119.
(5) TAKING OUT PRODUCT
After the above separating dies process is completed, the rapping bar 116 is projected from the surface of the movable die 112, so that a product 120 formed of an aluminum alloy is separated from the movable die 112.
In a conventional die casting method, to prevent bubbles from mixing in the product 120 (a faulty filling), the injection speed and the injection pressure at which the molten metal 117 is injected by the plunger 114 are respectively set as great as possible. In addition, after the molten metal 117 in the cavity has been completely coagulated and the alloy material has been completely shrunken, the movable die 112 is separated from the fixed die 111. Thus, in the conventional die casting machine, to completely coagulate the molten metal 117 in the cavity 119 as rapidly as possible, the fixed die 111 and the movable die 112 are respectively cooled by water or the like.
In the conventional die casting method, the aluminum alloy or the like is cast under a condition in which the injection speed and the injection pressure are respectively great, and after the alloy material is completely coagulated and shrunken in the dies, the movable die 112 is separated from the fixed die 111. Thus, when the movable die 112 is separated from the fixed die 111, the product (the cast good) is strongly adhering to the surfaces of the dies. As a result, to separate the movable die 112 from the fixed die 111 without deformation of the product and to smoothly take out the product from the die, it is required to form a draft angle on each die in the conventional die casting machine. For example, in a case where a pipe shaped product having an outer diameter 27 mm, an inner diameter 24 mm and a length 22 mm is cast by the die casting machine, at least a draft 0.5 with respect to the length 1=20 mm is required.
In the conventional die casting method and die casting machine, as a draft angle is formed on each die, after the product is taken out from the dies, a part of the product corresponding to the draft angle of the dies must be cut. Thus, the number of steps for manufacturing the product increases.
In addition, as the product which is strongly adhered to the surface of the die must be taken out from either of the dies without deformation thereof, it is difficult to manufacture thin products and products each having a complex shape. Further, as the die casting is carried out under a condition in which the injection speed and the injection pressure are respectively great, galling, deformation and the like are easily generated in the product.